BRATTLEBORO — Heavy traffic leaving the state Sunday after a long holiday weekend caused southbound backups of up to 4 miles on Interstate 91.

The Vermont Agency of Transportation is spending $59.5 million to remove and replace four interstate bridges between exits 2 and 3.

Some 20,000 daily drivers that used to have two lanes northbound and two lanes southbound now have one each. On Sunday, that caused tie-ups significant enough to cause authorities to send out press releases advising of the slowdown.

People seeking more information about the construction — set to continue through the summer of 2016 — can log onto its website, www.i91brattleborobridge.com.